1. Click Start, point to Administrative Tools, and then click DHCP.
2. Right-click the appropriate DHCP server or scope, and then click Properties.
3. Click DNS.
4. Click to select the Enable DNS dynamic updates according to the settings below check box to enable DNS dynamic update for clients that support dynamic update.

Note By default, this check box is selected.
5. To enable DNS dynamic update for DHCP clients that do not support it, click to select the Dynamically update DNS A and PTR records for DHCP clients that do not request for updates (for example, clients that are running Windows NT 4.0) check box.
6. Click OK.

Sorry to wake this old post, but I have the DNS issue, and the DHCP is not a Windows server, it is a router on a VPN site, and the DNS server is a datacenter in another subnet.
How to get CentOS to register itself in a Windows DNS server without having the same server being DHCP server?

Please don't resurrect 8 year old threads for a different version of the distro. Post a new thread in the relevant forum - CentOS 5 is dead and in any case, so dissimilar to CentOS 7 that any "fix" for 5 is unlikely to be applicable to 7.

CentOS 5 died in March 2017 - migrate NOW!
Full time Geek, part time moderator. Use the FAQ Luke